This invention is concerned with stents for supporting parts of blood vessels. More particularly it is concerned with stents such as supporting devices for arterial or venous grafts.
Stents are known devices used in surgery especially in vascular surgery for providing physical support to a blood vessel i.e. they can be used to help prevent kinking and/or collapse of blood vessels such as veins or arteries.
It has been proposed that vascular prostheses may incorporate non-planar curvature to improve blood flow velocity patterns by skewing the motion to induce xe2x80x98swirlxe2x80x99 flow to the blood circulating through the prosthesis.
We have now devised an apparatus and technique for establishing and/or maintaining non-planar curvature within arterial and/or venous grafts e.g. in blood vessel bypass surgery wherein the graft is a donor part from another blood vessel from the patient, which part is to be surgically connected to create a bypass in a blocked, constricted or otherwise blood flow-restricted vessel.
By maintaining non-planar curvature in the graft itself, favourable blood flow velocity patterns can be achieved through generation therein of xe2x80x98swirlxe2x80x99 flow. Failures in such grafts through blockage, kinking or collapse, can be significantly reduced.
According to this invention there is provided a stent for supporting part of a blood vessel which stent includes a supporting portion around which or within which part of a blood vessel intended for grafting can be placed so that the stent internally or externally supports that part and the supporting portion of the stent is of a shape and/or orientation whereby flow between graft and host vessel is caused to follow a non-planar curve.
The supporting portion of the stent may be fabricated to incorporate:
(i) a non-planar curved form and/or
(ii) a geometric arrangement of the junction between graft and host vessel e.g. artery whereby the tangent vector from the centreline of the graft does not intersect the centreline of the host vessel by consequence of an asymmetric disposition of the graft with respect to that host vessel at the junction with the graft.
The stent may be of generally hollow tubular shape with three dimensional curvature. The stent is particularly preferred for use in supporting such blood vessel parts as arterial and venous grafts, such as the living donor vessels. used in bypass surgery.
The stent may take the form of an open lattice generally tubular framework with discrete openings at each end thereof.
A blood vessel part such as an arterial graft may be passed through the interior section of e.g. a partially coiled tubular stent, which stent then provides support for that part of the graft which passes through its interior, and which thereby imparts to that graft a geometry which includes non-planar curvature i.e. the vessel part supported by the stent can assume and maintain curvature which is non-linear. Part of the supported vessel in such embodiments thereby acquires a geometry which can be regarded as a part-helical curve even if the physical extent of the supported vessel is less than one complete turn of a helix e.g. less than xc2xd or less than xc2xc of such a turn.
In other embodiments of the invention, the stent can comprise a first supporting structure adapted to support or otherwise contact part of the vessel to be bypassed, with a secondary supporting structure attached to and extending away from the first supporting structure, but simultaneously supporting the arterial or venous graft. The secondary such supporting structure may, for example, comprise a plurality of elongate members linked or connected in the region of their ends remote from the first supporting structure.
Such elongate members can be fabricated such that between them they define a curved section wherein the curvature is non-planar. Such an arrangement is particularly suited to an external stent for supporting the graft vessel at either or both physical junctions of the graft, as in a typical venous or arterial graft sites.
A practical embodiment of a non-planar internal stent is one fabricated from a shape memory alloy, formed to adept an appropriately helical or part-helical form, to provide the required support for the graft after insertion.